1. Field of the Invention
The invention relates to a heating system.
2. Related Art Statement
In a system for producing semiconductors, a ceramic heater may be provided for heating a wafer so as to deposit a semiconductor thin film on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like. A so called two-zone heater is known as such ceramic heater. Such two-zone heaters have a ceramic substrate and inner and outer resistance heat generators of a metal having a high melting point embedded within the substrate. Separate power supply terminals are connected to the respective heat generators so that electric power may be applied independently on the respective generators. The inner and outer heat generators may be thus independently controlled.
Further, in JP-A 5-326112, a resistance heat generator of a ceramic heater is constituted by plural circuit patterns, each made of a high melting point metal. The circuit patterns are so arranged that they may supplement one another's defect portions. For example, one of the patterns has a defect portion such as a folded portion or a returning portion. In this case, another circuit pattern is overlapped on or over the defect portion of the one pattern.
For example, in a heater used for heating semiconductor wafers, the temperature of the heating surface of the heater needs to be uniformly controlled over the entire surface. It is required that the heater satisfy a severe specification, for example, that the temperature measured on the heating surface is within ±10° C. on the whole heating surface under a use condition.
A ceramic heater is excellent on the viewpoint of uniformity of temperature on the heating face. Further, when a semiconductor wafer is mounted and heated, thermal deformation of the mounted face of the wafer over time may be prevented to preserve the flatness of the wafer at a low value.